Research On Frequency Deviation Estimation Algorithm Based On FFT

In the part of aerospace tracking,telemetering and command communicating system's receiver, coherent demodulation and doppler frequency speed measurement is one of the important tasks and one of the key function of the system. In the low SNR(signal-noise-ratio) and great doppler frequency shift to accomplish coherent demodulation and Doppler frequency speed measurement, the carrier wave frequency acquisition must be done, the key is how to estimate the frequency-deviation. In the thesis, the intermediate frequency signal's doppler frequency-deviation estimation algorithm based on FFT is studied.Firstly, this paper researches and analyses the principle of phase lock loop, three carrier tracking loop-the square loop, castas loop and digital phase lock loop and their advantage and application scope.Secondly, the paper introduces the digitization technology of intermediate frequency receiver, including signal sampling and decimation technology, then introduces the real signal digital mixing orthogonality alternation. that provides theory basis for the project's design, simulation and realization.Finally, the paper analyzes the variation of SNR after FFT transformation from time domain to frequency domain. On this basis, designs a frequency-deviation estimation algorithm based on FFT (Fast Fourier Transform), that can accurately estimate the polarity and absolute value of carrier doppler frequency-deviation, the threshold of lowest C/N is -38dB, the range of frequency-deviation estimation is±350kHz. The result of matlab simulating proves the analyzing conclusion is proper. Then, with DSP technology, FFT carrier acquisition arithmetic is programmed, debugged and simulated in the CCS, the carrier acquisition algorithm is downloaded in TMS320C6416 software simulator to run. The result is consistent with the practical data. It proves that the carrier acquisition arithmetic proposed in this thesis is availability.